Removal of sulfate from industry wastewater by double salt method

Removal of sulfate from industry wastewater containing sulfate with high concentration were studied using hydrated aluminum salt and lime milk as remover. The effects of solution pH value, aluminum salt dosage, reaction time, initial concentration of SO 24- and reaction temperature on the removal of SO 24- were also investigated, and three factors and three levels orthogonal experiments were designed. The results determined by single factor and orthogonal experiments indicate that the optimum conditions for the removal of sulfate are as follows: reaction temperature is 25 ℃, reaction time is 60 min, pH value of solution is 11, the molar ratio of sulfate to aluminum is 1.1-1.0, and the influencing sequence of each factor from large to small is solution pH value, aluminum salt dosage, reaction time. By comparison between the wastewater and the purified water, the sulfate concentration decreased sharply from 1 720 mg/L to 100 mg/L or below under the optimum conditions, which is less than hygienic standard for drinking water. The X-ray diffraction pattern of the precipitation shows that the main composition of the solid phase is ettringite (Ca6Al2(SO4)3(OH)12·26H2O).